During the 1957-59 period, the B & M transitioned from a mix of conventional and RDC runs out of Boston to all RDC (State of Maine Route & Connecticut River Line lasted a few years longer with conventional equipment). During this period there were numerous schedule changes. One of the consist sheets I have has the early morning mail and paper train towing an RDC from Boston to Concord, NH. This RDC then made a quick round-trip to Plymouth, NH and back at Concord it was coupled up to an RDC from White River, Jct. for the run back to Boston. I also believe sbout the same time, an RDC was towed from Boston to Greenfield, Mass. and then set free and it ran to Williamstown and then all the way back to Boston.
On the Boston & Albany, I remember seeing mail-express-passenger train #18, later #400, towing up to four RDCs, Springfield to Boston, usually Sundays. This would be 1957-1959.
During 1962-63 I attended Northeastern University in Boston and all the classrooms at the back of the buildings had a great view of the New Haven's Boston-Providence-New York mainline. Mail #182 sometimes had an RDC coupled on as the crew car, probably from New Haven.
The C&EI Meadowlark was an RDC from about 1956 onward and on busy travel days towed a lightweight coach as part of its trains.